New Zealand scaup

New Zealand scaup are gregarious diving ducks common throughout New Zealand. Compact and blackish, they have the silhouette of a bath-toy duck. Large approachable flocks are a feature of the Rotorua and Queenstown lakeshores, and scaup are also common on the Avon River that flows through Christchurch.

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Identification

New Zealand scaup are quite unlike any other resident duck species. Dark and squat with a rounded profile, they often occur in large flocks, floating with cork-like buoyancy. Scaup are diving ducks and spend a lot of time underwater, where they can travel considerable distances. Both sexes are dark-plumaged, but are easily distinguished. The male has dark black-brown plumage with iridescent blue-green head and wings, and lighter mottling on the chest and underparts. His iris is yellow and bill blue-grey. The female is a duller chocolate brown, paler on her underparts. Her iris is brown and bill grey, normally with a ring of white feathers at the base. Juvenile resemble females until 12 weeks-old when the male iris colour becomes yellow. In flight, all birds have a broad white upper-wing bar and pale white underwing. Scaup have a fast wing beat and often fly just above the water. They sometimes rest on land, but quickly retreat to water when disturbed.

Voice: males have a high pitched whistle call weeee weo-weo weo-weo weo-weoooo. The female call is a low quiet wack wack.

Similar species: brown teal are a similar size but have a long, flat body. Vagrant Australian white-eyed ducks are larger and have white undertail coverts. Males also have white eyes and both sexes have a pale saddle on the upper mandible. Australian coots are similar in body size, shape, colouration and diving behaviour, but have a bright white bill and frontal shield.

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Distribution and habitat

New Zealand scaup are widely but patchily distributed throughout the North and South Islands. They are found on dune lakes in Northland and Manawatu, and on inland lakes in Waikato, Taupo, Rotorua and Hawke’s Bay. In the South lsland they are common on West Coast lakes, north Canterbury waterways (including Christchurch), and eastern and southern high country and hydroelectric lakes. They are common on large, deep, freshwater lakes, including hydro-electric lakes, and are becoming increasingly common on shallow lowland lakes, slow flowing rivers and salt water. They are not found on Stewart Island, and are no longer present on Chatham Islands.

Scaup often congregate in sheltered areas near willows or reed beds, moving as wind conditions change; although they have favoured locations. They are considered non-migratory despite being capable fliers. Their numbers can fluctuate greatly on otherwise preferred lakes, suggesting at least some localised seasonal movements. Movement is also driven by ice conditions during winter.

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Population

The New Zealand scaup population was estimated at 20,000 birds in the 1990s. This may have increased following the range and population expansion reported in Canterbury.

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Threats and conservation

Populations apparently declined during late 1800s and early 1900s due to land clearance, associated hydrological changes, predation and hunting. Adults and chicks are vulnerable to predation during nesting and chick-rearing which may result in low breeding success. Predator control and provision of suitable feeding and breeding habitat has led to population expansion at Bromley Oxidation Ponds and Te Huingi Manu Wildlife Refuge in Christchurch. The success of this one site has probably allowed the recolonisation of the wider Christchurch area.

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Breeding

The nest is well concealed on the ground close to the water. Nests may be partially open above, or covered, or have a tunnel leading to a concealed chamber. The nest is a tidy bowl consisting of the surrounding materials, and lined with a layer of down. Breeding mainly occurs between October and March. They nest solitary or in a loose colony. Only females incubate and care for young, but solitary males, or groups of males are often reported close to breeding sites. Chicks often form crèches.

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Behaviour and ecology

There have been few studies on the behaviour or ecology of scaup. They are social, and can form dense rafts especially in autumn and winter and are often associated with other species particularly coots, shoveler and crested grebes. A range of male courtship behaviours were documented by Stoke (1991) including “sneak” (neck extended), “head-flicks” (rapid upwards head and bill movement) and “kink-neck” (neck held at unusual angle). Aggressive displays occur between courting males. Several males attend females until a bond has established, the bonded male will defend the female and they separate themselves from the group. Pairs form at the breeding site and last only until the female begins nesting when the bond apparently breaks. Females have been recorded laying in the nests of other females at one well-studied population (Lake Clearwater, inland Canterbury)

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Food

Scaup obtain most of their food by diving. Prey items include snails, chironomid larvae and caddisfly larvae. Plant material is probably taken also.